Overvoltage protection

ABSTRACT

The present disclosure relates to a device including a rectifying bridge including: a branch connected between first and second nodes; another branch including first and second MOS transistors series-connected between the first and second nodes and having their sources coupled together; a resistor connecting the gate of the first transistor to the second node; another resistor connecting the gate of the second transistor and the first node; and for each transistor, a circuit including first and second terminals respectively connected to the drain and to the gate of the transistor, and being configured to electrically couple its first and second terminals when a voltage between the first terminal of the circuit and the first terminal of the other circuit is greater than a threshold of the circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of French Application No. 20/01096,filed on Feb. 4, 2020, which application is hereby incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure generally relates to electronic circuits and,more particularly, to a protection against overvoltages capable ofoccurring between pads of such electronic circuits, particularly afteran electrostatic discharge.

BACKGROUND

Wireless communication devices capable of communicating by means ofelectromagnetic waves, for example, by means of radio frequency waves.When an antenna of a first device receives an electromagnetic waveemitted by a second device, the power received by the antenna of thefirst device may be used to electrically power circuits, for example,integrated circuits, of the first device. For this purpose, the firstdevice generally comprises a rectifying voltage bridge configured toreceive a voltage available between two pads or terminals coupled to therespective ends of a conductive winding of the antenna of the firstdevice, and to deliver a rectified power supply voltage.

However, overvoltages, for example, caused by electrostatic discharges,may occur between the two pads coupled to the respective ends of theconductive winding of the antenna. Such overvoltages are capable ofdeteriorating, or even of destroying, circuits of the first devicecoupled to at least one of the two pads, particularly the rectifyingbridge which is coupled to the pads.

SUMMARY

There is a need to overcome all or part of the disadvantages of knownwireless communication devices, particularly as concerns the protectionof such devices against overvoltages, for example, caused byelectrostatic discharges, capable of occurring between pads coupled tothe respective ends of a conductive winding of an antenna.

An embodiment overcomes all or part of the disadvantages of knownwireless communication devices.

An embodiment overcomes all or part of the disadvantages of knownwireless communication devices, which are due to overvoltages, forexample, caused by electrostatic discharges, capable of occurringbetween pads coupled to the respective ends of a conductive winding ofan antenna of these devices.

An embodiment overcomes all or part of the disadvantages of knownvoltage rectifying bridges configured to rectify a voltage availablebetween two pads coupled to the respective ends of a conductive windingof an antenna of a wireless communication device.

An embodiment provides a device comprising a rectifying bridgecomprising: a first branch connected between first and second inputnodes of the bridge and comprising a third output node of the bridge; asecond branch comprising first and second MOS transistorsseries-connected between the first and second nodes, the sources of thefirst and second transistors being coupled to a fourth output node ofthe bridge; a first resistor connected between the gate of the firsttransistor and the second node; a second resistor connected between thegate of the second transistor and the first node; and for each of thefirst and second transistors, a circuit associated with the transistorand comprising a first terminal connected to the drain of the transistorand a second terminal connected to the gate of the transistor, thecircuit being configured to electrically couple its first and secondterminals when an absolute value of a voltage between the first terminalof the circuit and the first terminal of the other circuit is greaterthan or equal to an absolute value of a threshold of the circuit and thevoltage has the same sign as the threshold.

According to an embodiment, each circuit is further configured toelectrically isolate its first and second terminals when the absolutevalue of the voltage between the first terminal of the circuit and thefirst terminal of the other circuit is smaller than the absolute valueof the threshold of the circuit and also when the voltage has a signopposite to the sign of the threshold of the circuit.

According to an embodiment, the first branch of the bridge comprisesthird and fourth MOS transistors series-connected between the first andsecond node and each diode-assembled, the sources of the third andfourth transistors being connected to the third node.

According to an embodiment, the first, second, third, and fourthtransistors have a same N or P channel.

According to an embodiment, each circuit comprises a branch comprising afirst dipole with a diode function and a second dipole with a diodefunction coupled in anti-series, an end of the branch being connected tothe first terminal of the circuit and another end of the branch beingcoupled to the first terminal of the other circuit.

According to an embodiment, in each circuit, the first and seconddipoles are configured to block a current when the absolute value of thevoltage between the first terminal of the circuit and the first terminalof the other circuit is smaller than the absolute value of the thresholdof the circuit and when the voltage has a sign opposite to the sign ofthe threshold of the circuit, and to conduct a current when the absolutevalue of the voltage between the first terminal of the circuit and thefirst terminal of the other circuit is greater than or equal to theabsolute value of the threshold of the circuit and the voltage has thesame sign as the threshold.

According to an embodiment, each circuit is configured so that theconduction of the current in the first dipole of the circuit causes anelectric coupling of the first and second terminals of the circuit.

According to an embodiment, in at least one of the circuits, preferablyin each circuit, the other end of the branch of the circuit is connectedto the second terminal of the circuit.

According to an embodiment, in the at least one of the circuits,preferably, in each circuit, the branch of the circuit comprises: fifth,sixth, and seventh nodes; a third resistor series-connected to the firstdipole between the fifth node and the sixth node; and a fourth resistorconnected between the sixth node and the seventh node, each circuitfurther comprising a transistor having a control terminal connected tothe sixth node and having conduction terminals respectively connected tothe fifth node and to the seventh node, a voltage drop in the fourthresistor conditioning a turning-on of the transistor.

According to an embodiment, in the at least one of the circuits,preferably in each circuit: the second dipole is connected between thefirst terminal of the circuit and the fifth node, the seventh node beingconnected to the second terminal of the circuit; or the second dipole isconnected between the seventh node and the second terminal of thecircuit, the fifth node being connected to the first terminal of thecircuit; or the second dipole is connected between the first terminal ofthe circuit and the seventh node, the fifth node being connected to thesecond terminal of the circuit; or the second dipole is connectedbetween the fifth node and the second terminal of the circuit, theseventh node being connected to the first terminal of the circuit.

According to an embodiment, in at least one of the circuits, preferablyin each circuit, the other end of the branch of the circuit is connectedto a third terminal of the circuit, the third terminal of the circuitbeing connected to the first terminal of the other circuit.

According to an embodiment, in the at least one of the circuits,preferably in each circuit, the branch comprises a third resistor inseries with the first and second dipoles, each circuit furthercomprising a transistor having a control terminal connected to aterminal of the third resistor, having a first conduction terminalcoupled to the first terminal of the circuit, and having a secondconduction terminal coupled to the second terminal of the circuit, avoltage drop in the third resistor conditioning a turning-on of thetransistor.

According to an embodiment, in the at least one of the circuits,preferably in each circuit, the second dipole is connected between thefirst terminal of the circuit and the first conduction terminal of thetransistor, the second conduction terminal of the transistor beingconnected to the second terminal of the circuit.

According to an embodiment, at least one of the circuits, preferablyeach circuit, further comprises a third dipole with a diode functionseries-connected to the transistor of the circuit between the first andsecond terminals of the circuit, the third dipole being connected to thesecond terminal of the circuit and the branch of the circuit beingconnected between the first and third terminals of the circuit.

According to an embodiment, the first dipole is formed of a Zener diode,of an assembly of a plurality of Zener diodes connected in parallel toone another, or of an assembly of a plurality of series-connected MOStransistors, each being diode-assembled.

Another embodiment provides an integrated circuit comprising a devicesuch as described.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and advantages, as well as others, will bedescribed in detail in the following description of specific embodimentsgiven by way of illustration and not limitation with reference to theaccompanying drawings, in which:

FIG. 1 illustrates, in the form of a circuit, a portion of a devicecomprising an example of a rectifying bridge;

FIG. 2 shows a plurality of curves illustrating different MOS transistorturn-on operations;

FIG. 3 illustrates, in the form of a circuit, a portion of a devicecomprising a rectifying bridge according to an embodiment;

FIG. 4 illustrates in the form of a circuit a portion of a devicecomprising a rectifying bridge according to another embodiment;

FIG. 5 illustrates in the form of a circuit a portion of a devicecomprising a rectifying bridge according to still another embodiment;and

FIG. 6 illustrates, in the form of a circuit, a portion of a devicecomprising a rectifying bridge according to still another embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Like features have been designated by like references in the variousfigures. In particular, the structural and/or functional features thatare common among the various embodiments may have the same referencesand may dispose identical structural, dimensional and materialproperties.

For the sake of clarity, only the steps and elements that are useful foran understanding of the embodiments described herein have beenillustrated and described in detail. In particular, the various wirelesscommunication protocols, particularly by radio frequency waves, andtheir implementations have not been detailed, the described embodimentsbeing compatible with known wireless communication protocols and knownimplementations of such protocols. Further, the functions implemented byknown devices comprising a voltage rectifying bridge coupled to two padsof the device between which a voltage to be rectified is available havenot been described, the described embodiments being compatible withusual functions of such known devices.

Unless indicated otherwise, when reference is made to two elementsconnected together, this signifies a direct connection without anyintermediate elements other than conductors, and when reference is madeto two elements coupled together, this signifies that these two elementscan be connected or they can be coupled via one or more other elements.

In the following disclosure, unless indicated otherwise, when referenceis made to absolute positional qualifiers, such as the terms “front”,“back”, “top”, “bottom”, “left”, “right”, etc., or to relativepositional qualifiers, such as the terms “above”, “below”, “higher”,“lower”, etc., or to qualifiers of orientation, such as “horizontal”,“vertical”, etc., reference is made to the orientation shown in thefigures.

Unless specified otherwise, the expressions “around”, “approximately”,“substantially” and “in the order of” signify within 10%, and preferablywithin 5%.

In the following description, unless otherwise indicated, all thepotentials and the voltages are referenced with respect to a samereference potential, typically ground GND or, in other words, a zeroreference voltage.

FIG. 1 illustrates, in the form of a circuit, a portion of a device 1comprising an example of a rectifying bridge 2.

In this example, device 1 is a wireless communication device comprisinga conductive antenna winding, or inductance or coil, not shown, havingits ends respectively connected to a pad, or terminal, 101, and to apad, or terminal, 102 of device 1. In the following description, thecase where device 1 is a radio frequency communication device, forexample, a near-field communication or NFC device 1, is considered as anexample.

A MOS transistor (“Metal Oxide Semiconductor”) with an N channel (notshown) may be connected between pads 101 and 102, for example, toimplement a function of retromodulation of an electromagnetic fieldreceived by the antenna of device of device 1. The retromodulation MOStransistor has a first conduction terminal, for example, its source,coupled, preferably connected, to pad 102, and a second conductionterminal, for example, its drain, coupled, preferably connected, to pad101.

A capacitor (not shown) may be provided between pads 101 and 102, forexample, to adjust the resonance frequency of the antenna of device 1.

FIG. 1 more particularly shows the voltage rectifying bridge 2 of device1.

Bridge 2 is coupled to pads 101 and 102 to receive a voltage Vin to berectified. Voltage Vin corresponds to the difference between thepotential of node 102 and that of node 101, and is, in the presentexample, referenced with respect to node 101. As an example, voltage Vinhas a maximum amplitude smaller than 6 V, for example, equal to 5.5 V(voltage Vin for example ranging from −5.5 V to +5.5 V).

Rectifying bridge 2 is configured to deliver a rectified power supplyvoltage Vout to circuits (not shown) of device 1. Voltage Voutcorresponds to the difference between the potential of an output node206 of bridge 2 and that of an output node 210 of bridge 2, and is, inthe present example, referenced with respect to node 210. In thisexample, node 210 is at reference potential GND, typically the ground.

Rectifying bridge 2 comprises two nodes, or terminals, 201 and 202coupled to respective pads 101 and 102. In the illustrated example,nodes 201 and 202 are connected to respective pads 101 and 102.According to another example, not illustrated, node 201, respectively202, is coupled to pad 101, respectively 102, by a resistor of lowvalue, typically a few Ohms.

Rectifying bridge 2 comprises two branches connected in parallel betweeninput nodes 201 and 202.

One of the two branches comprises two N-channel MOS transistors 203 and204 series-connected between nodes 201 and 202. Transistors 203 and 204are connected to each other at the level of node 206 of bridge 2 or, inother words, each of transistors 203 and 204 is connected to node 206.Each transistor 203, 204 is diode-assembled, that is, its gate and itsdrain are connected to each other. In the shown example, transistor 203has its drain and its gate connected to node 202, transistor 204 havingits drain and its gate connected to node 201, and the sources oftransistors 203 and 204 being connected to node 206 or, in other words,being connected together at the level of node 206.

According to another example, not illustrated, each of transistors 203and 204 may be replaced with a diode, for example, by replacingtransistor 203 with a diode having its anode connected to node 202 andhaving its cathode connected to node 206, and transistor 204 withanother diode having its anode connected to node 201 and having itscathode connected to node 206.

The other one of the two branches of rectifying bridge 2 comprises twoN-channel MOS transistors 208 and 209 series-connected between nodes 201and 202. Transistors 208 and 209 are connected to each other at thelevel of the node 210 of rectifying bridge 2 or, in other words, each oftransistors 208 and 209 is connected to node 210. As an example,transistor 208 has its drain connected to node 202, its source connectedto node 210, and its gate connected to node 201, transistor 209 havingits drain connected to node 201, its source connected to node 210, andits gate connected to node 202.

Transistors 208 and 209 have their body regions or channel-formingregions coupled, preferably connected, to node 210, to be at thepotential of node 210.

In operation, when an AC voltage Vin is available between pads 101 and102, and thus, in the present example, between nodes 201 and 202,rectifying bridge 2 delivers rectified voltage Vout. In particular, whenthe potential of node 202 is sufficiently greater than that of node 201,transistors 203 and 209 are on and transistors 204 and 208 are off.Conversely, when the potential of node 201 is sufficiently greater thanthat of node 202, transistors 203 and 209 are off and transistors 204and 208 are on.

It is considered that an overvoltage occurs between pads 102 and 101,and thus between nodes 201 and 202, such an overvoltage for examplecorresponding to an increase in the potential of pad 102 with respect tothat of pad 101, or positive overvoltage. A positive overvoltage forexample results from an electrostatic discharge on pad 102, for example,an electrostatic discharge of 1.5 kV, or even 2 kV, according to thehuman body model or HBM. Such an electrostatic discharge is for examplecaused by a person touching pad 102 or the conductive antenna winding ofdevice 1 which is coupled to pad 102.

Such a positive overvoltage between pads 102 and 101 causes the flowingof a significant current, for example, of at least 1 A, between pads 102and 101, for example, a positive current flowing from pad 102 to node210 via transistor 208, and from node 210 to pad 101 via theforward-biased diode between the substrate (body) and the drain oftransistor 209.

Since the gate and the source of transistor 208 are substantially at thesame potential, that is, that of node 210, transistor 208 should be off.However, when the potential difference between the drain and the sourceof MOS transistor 208 exceeds a threshold, called snapback threshold,the parasitic bipolar transistor of MOS transistor 208 starts conductingand a current flows from the drain to the source of MOS transistor 208.Such a current then flows to node 201, via the forward diode between thebody (substrate) region and the drain of transistor 209. The conductionof the current between the drain and the source of transistor 208 has,between the conduction terminals of transistor 208, a negativedifferential impedance, which raises an issue.

An example of such an issue arises when MOS transistor 208 isimplemented by means of a plurality of elementary MOS transistorsconnected in parallel. Indeed, due to manufacturing dispersions, thesnapback threshold of a first one of these elementary transistors may belower than that of all the other elementary transistors. As a result,the turning-on of the parasitic bipolar transistor of the firstelementary MOS transistor occurs before the turning-on of the parasiticbipolar transistors of the other elementary MOS transistors. All thecurrent flowing through MOS transistors 208 then flows through the firstelementary MOS transistor, which may result in a deterioration, or evenin a destruction, of the first elementary MOS transistor.

Although this is not detailed, the problems illustrated hereinabove inrelation with transistor 208 during a positive overvoltage between pads102 and 101 are posed in symmetrical fashion for transistor 209 duringan overvoltage between pads 102 and 101 corresponding to an increase inthe potential of node 201 with respect to the potential of node 202, ornegative overvoltage.

To overcome all or part of the disadvantages of rectifying bridge 2, theinventor here provides associating, with each of transistors 208 and209, a so-called turn-on circuit, having first and second terminalsrespectively connected to the drain and to the gate of the transistor208 or 209 having the circuit associated therewith. Further, a resistoris connected between the gate of transistor 208 and node 201 (drain oftransistor 209), another resistor being connected between the gate oftransistor 209 and node 202 (drain of transistor 208).

Each of the turn-on circuits is configured to electrically couple itsfirst and second terminals when a voltage between its first terminal andthe first terminal of the other circuit is greater than or equal to athreshold of the circuit. In other words, a first one of the turn-oncircuits associated with transistor 208 is configured to electricallycouple its first and second terminals when the voltage between its firstterminal (drain of transistor 208-node 202) and the first terminal(drain transistor 209-node 201) of the second turn-on circuit associatedwith transistor 209 exceeds the threshold of the first circuit, thesecond circuit being configured to electrically couple its first andsecond terminals when the voltage between its first terminal and thefirst terminal of the first circuit exceeds the threshold of the secondcircuit. The exceeding of the considered turn-on threshold by thevoltage between the first terminal of this circuit and the firstterminal of the other circuit is indicative of an overvoltage betweennodes 201 and 202.

Further, each of the turn-on circuits is configured to electricallyisolate or decouple its first and second terminals from each other whenthe voltage between the first terminal of the circuit and the firstterminal of the other circuit is smaller than the threshold of thecircuit. In other words, the first circuit is configured to electricallyisolate its first and second terminals when the voltage between itsfirst terminal and the first terminal of the second circuit is smallerthan the threshold of the first turn-on circuit, the second circuitbeing configured to electrically isolate its first and second terminalswhen the voltage between its first terminal and the first terminal ofthe first circuit is smaller than the threshold of the second circuit.Thus, in the absence of an overvoltage between nodes 201 and 202, theoperation of the rectifying bridge is not modified by the presence ofthe turn-on circuits and operates similarly to the rectifying bridge 2described in relation with FIG. 1.

In the following description and in the claims, the term dipole with adiode function designates a component or a circuit having two terminalsbetween which the component or circuit behaves as a diode. One of theterminals of the dipole is called cathode of the dipole and the otherterminal of the dipole is called anode of the dipole. The dipole has,between its anode and its cathode, the same behavior as that that adiode would have between its anode and its cathode, respectively.

According to an embodiment, each turn-on circuit comprises a branchcomprising a first dipole with a diode function and a second dipole witha diode function coupled in anti-series, an end of this branch beingconnected to the first terminal of the turn-on circuit and another endof the branch being coupled to the first terminal of the other turn-oncircuit. The term branch comprising first and second dipoles with adiode function coupled in anti-series designates the case where, in thebranch, the first and second dipoles have their anodes coupled together,or have their cathodes coupled together.

According to an embodiment, each turn-on circuit comprises a thirdterminal connected to the first terminal of the other circuit. In suchan embodiment, in each turn-on circuit, the branch comprising the firstand second dipoles in anti-series is connected between the first andthird terminals of the circuit or, in other words, one end of the branchis connected to the first terminal of the circuit and another end of thebranch is connected to the third terminal of the circuit.

According to another embodiment, in each turn-on circuit, the branchcomprising the first and second dipoles in anti-series is connectedbetween the first and second terminals of the circuit or, in otherwords, one end of the branch is connected to the first terminal of thecircuit and another end of the branch is connected to the secondterminal of the circuit.

According to an embodiment, in each turn-on circuit, the first andsecond dipoles are configured to block a current when the voltagebetween the first terminal of the circuit and the first terminal of theother circuit is smaller than the threshold of the circuit.

According to an embodiment, in each turn-on circuit, the first andsecond dipoles are further configured to conduct a current when thevoltage between the first terminal of the circuit and the first terminalof the other circuit is greater than or equal to the threshold of thecircuit.

According to an embodiment, each turn-on circuit is configured so thatthe conduction of a current in the first dipole of the circuit causes anelectric coupling of the first and second terminals of the circuit.

According to an embodiment, in each turn-on circuit, a forward turn-onthreshold of the second dipole and a reverse turn-on threshold of thefirst dipole at least partly determine the threshold of the turn-oncircuit. The term forward turn-on threshold of a dipole with a diodefunction designates a value of the voltage of the dipole anode,referenced with respect to the dipole cathode, above which the dipoleconducts a positive current from its anode to its cathode. Similarly,the term reverse turn-on threshold of a dipole with a diode functiondesignates a value of the voltage of the dipole cathode, referenced withrespect to the dipole anode, above which the dipole conducts a positivecurrent from its cathode to its anode.

FIG. 2 shows curves C0, C2, C3, C4, C5, and C6 illustrating differentturn-on occurrences of a MOS transistor, in this example, with an Nchannel. Each curve illustrates the variation of a current Is betweenthe drain and the source of the transistor when the source of thetransistor is at ground GND and the potential Vd of the transistor drainincreases. Each curve corresponds to a different potential applied tothe transistor gate.

Curve C0 of FIG. 2 illustrates the case where the potential applied tothe transistor gate is zero or, in other words, is equal to groundpotential GND. When the drain potential Vd of the transistor increasesbeyond the transistor snapback threshold Vsb, the transistor then has,between its conduction terminals, a negative differential impedance.More particularly, as long as potential Vd is below threshold Vsb,current Is is zero or next to zero. Further, after potential Vd hasreached threshold Vsb, a non-zero current Is flows through thetransistor, current Is increasing at the same time as potential Vddecreases due to the negative differential impedance of the transistor.

Curves C2, C3, C4, C5, and C6 illustrate cases where the potentialapplied to the transistor gate is non-zero, this potential being higherfor curve C3 than for curve C2, higher for curve C4 than for curve C3,higher for curve C5 than for curve C4, and higher for curve C6 than forcurve C5.

It can be observed that for the case of curve C2, the consideredtransistor still has a negative differential impedance, that is, thecurve has a portion where current Is increases while potential Vddecreases but the value of the negative impedance is smaller than in thecase of curve C0. For the case of curves C3, C4, C5, and C6, such anegative differential impedance is suppressed.

It can further be observed that the higher the potential on the gate ofthe transistor, the lower the maximum value that potential Vd can take.

It can also be observed that the higher the potential on the transistorgate, the higher the value of current Is for a given potential value Vd.

Thus, the provision of turn-on circuits associated with respectivetransistors 208 and 209 enables, during an overvoltage between nodes 201and 202 causing an increase in the drain potential of one of thetransistors, the turn-on circuit associated with the transistor to causea corresponding increase of the gate potential of the transistor. As aresult, the transistor then operates as illustrated by curves C3, C4,C5, and C6 and no longer has a negative differential impedance. Further,for a given drain potential, the higher the gate potential of thistransistor will be during an overvoltage between nodes 201 and 202, thehigher the current Is flowing between the conduction terminals of thetransistor, thus allowing a more efficient protection against theovervoltage.

Several embodiments and variations of turn-on circuits will now bedescribed in relation with FIGS. 3 to 6.

FIG. 3 illustrates, in the form of a circuit, a portion of a device 3comprising a rectifying bridge 4 provided with turn-on circuitsaccording to an embodiment.

Device 3 is similar to the device 1 of FIG. 1, only the differencesbetween devices 1 and 3 being here detailed.

More particularly, device 3 differs from device 1 by its voltagerectifying bridge 4, different from voltage rectifying bridge 2. Ascompared with rectifying bridge 2, rectifying bridge 4 comprises aresistor R1 connected between node 201 and the gate of transistor 208,and a resistor R2 connected between node 202 and the gate of transistor209. Rectifying bridge 4 further differs from rectifying bridge 2 inthat it comprises, for each of transistors 208 and 209, a turn-oncircuit 300 associated with the transistor. Each circuit 300 comprises afirst terminal 301 and a second terminal 302. The circuit 300 associatedwith transistor 208, respectively 209, has its terminal 301 connected tothe drain of transistor 208, respectively 209, and its terminal 302connected to the gate of transistor 208, respectively 209.

Each circuit 300 comprises a branch comprising a first dipole with adiode function D1 and a second dipole with a diode function D2 coupledtogether in anti-series.

In the embodiment illustrated in FIG. 3, in each circuit 300, the branchcomprising dipoles D1 and D2 in anti-series is connected betweenterminals 301 and 302 of the circuit or, in other words, has one endconnected to the terminal 301 of circuit 300 and another end connectedto the terminal 302 of circuit 300.

In the example of FIG. 3, in each circuit 300, dipoles D1 and D2 havetheir cathodes connected together and their anodes connected toterminals 301 and 302, respectively. In another example, not shown, ineach circuit 300, dipoles D1 and D2 have their anodes connected togetherand their cathodes connected to terminals 301 and 302, respectively.

The normal operation of bridge 4, that is, in the absence of anovervoltage between nodes 201 and 202, is the following. Due to theabsence of an overvoltage between nodes 201 and 202, the voltage betweennodes 202 and 201 (voltage of node 202 referenced to node 201) issmaller than the threshold of the circuit 300 associated with transistor208, and the voltage between nodes 201 and 202 (voltage of node 201referenced to node 202) is smaller than the threshold of the circuit 300associated with transistor 209. The dipoles D1 and D2 of the circuit 300associated with transistor 208, respectively 209, then block the flowingof a current between the terminals 301 and 302 of the circuit associatedwith transistor 208, respectively 209, and through resistor R1,respectively R2. As a result, the potential of node 202, respectively201, is present on the gate of transistor 209, respectively 208.

More particularly, in the example of FIG. 3, when the potential of node202 is greater than the potential of node 201, the dipole D2 of thecircuit 300 associated with transistor 209 is reverse biased and isequivalent to an open circuit. Further, the dipole D1 of the circuit 300associated with transistor 208 is also reverse-biased, but the voltagethereacross is smaller than its reverse turn-on voltage, whereby dipoleD2 is equivalent to an open circuit. Further, as soon as the voltagebetween node 202 and node 201 becomes greater than the threshold voltageof transistor 209, the latter switches to the on state and electricallycouples node 201 to node 210, transistor 208 being in the off state.

The normal operation of bridge 4 when the potential of node 201 isgreater than that of node 202 can be deduced, by symmetry, from theabove-described operation.

The operation of bridge 4 during an overvoltage between nodes 201 and202 is the following. The case of a positive overvoltage is consideredas an example. Transistor 209 and its associated circuit 300 then behaveas in normal operation or, in other words, the circuit 300 associatedwith transistor 209 is equivalent to an open circuit between itsterminals 301 and 302, and transistor 209 is on. Further, as soon as thevoltage between node 202 and node 201 becomes greater than the thresholdof the circuit 300 associated with transistor 208, a current flowsthrough dipoles D1 and D2 of the circuit and through resistor R1. As aresult, the gate potential of transistor 208 increases with thepotential of node 202. In other words, the potential on the gate oftransistor 208 is then equal to the potential of node 202 minus thevoltage drop in the dipoles D1 and D2 of the circuit 300 associated withtransistor 208. In the example of FIG. 3, the threshold of each circuit300 is equal to the sum of the reverse turn-on threshold of dipole D1and of the forward turn-on threshold of dipole D2.

The operation of bridge 4 in case of a negative overvoltage betweennodes 201 and 202 can be deduced, by symmetry, from the operationdescribed hereinabove in case of a positive overvoltage.

FIG. 4 illustrates, in the form of a circuit, a portion of a device 3-1comprising a rectifying bridge 4-1 according to another embodiment.

Device 3-1 is similar to the device 3 of FIG. 3, only the differencesbetween devices 3-1 and 3 being here detailed. More particularly, device3-1 differs from device 3 by its voltage rectifying bridge 4-1,different from voltage rectifying bridge 4, rectifying bridge 4-1comprising a turn-on circuit 300-1 instead of each circuit 300 ofrectifying bridge 4. Each circuit 300-1 comprises a first terminal 301and a second terminal 302. The circuit 300-1 associated with transistor208, respectively 209, has its terminal 301 connected to the drain oftransistor 208, respectively 209, and its terminal 302 connected to thegate of transistor 208, respectively 209.

Each circuit 300-1 comprises a branch comprising a first dipole with adiode function D1 and a second dipole with a diode function D2 coupledtogether in anti-series.

In the embodiment illustrated in FIG. 4, in each circuit 300-1, thebranch comprising dipoles D1 and D2 in anti-series is connected betweenterminals 301 and 302 of the circuit. In each circuit 300-1, the branchcomprising dipoles D1 and D2 in anti-series further comprises a resistorR3 series-connected to the first dipole D1 between node 401 and a node402, and a resistor R4 connected between node 402 and a node 403. Eachcircuit 300-1 further comprises a transistor T having a control terminalconnected to node 402 and having conduction terminals respectivelyconnected to terminals 401 and 403. Each circuit is configured so that avoltage drop in its resistor R4 conditions a turning-on of itstransistor T.

According to an embodiment, as illustrated in FIG. 4, in each circuit300-1, transistor T is a P-channel MOS transistor, the source and thedrain of transistor T then being coupled, preferably connected, to nodes403 and 401, respectively. Preferably, the body region of transistor Tis coupled to the source of transistor T, so that the body and sourceregions of transistor T are at the same potential.

In an alternative embodiment, not illustrated, in each circuit 300-1,transistor T is replaced with a PNP bipolar transistor having its baseforming a control terminal of the transistor and connected to node 402,having its emitter connected to node 403, and having its collectorconnected to node 401.

According to an embodiment, as illustrated in FIG. 4, in each circuit300-1, dipole D2 is connected between node 401 and the terminal 302 ofcircuit 300-1. More particularly, in the present example, the cathode ofdipole D2 is connected to the terminal 302 of circuit 300-1. Node 403 isthen, in the present example, connected to terminal 301. In analternative embodiment, not illustrated, in each circuit 300-1, dipoleD2 is connected between terminal 301 and the node 403 of circuit 300-1.More particularly, the anode of dipole D2 is for example connected tothe terminal 301 of circuit 300-1, node 401 being for example connectedto terminal 302.

The normal operation of bridge 4-1 is similar to that of thepreviously-described bridge 4 (FIG. 3). In particular, in each circuit300-1, when no current flows through the dipoles D1 and D2 of circuit300-1, the voltage across resistor R4 is zero, and transistor T is off.Thus, no current flows between the terminals 301 and 302 of circuits300-1, nor through resistors R1 and R2.

The operation of bridge 4 during an overvoltage between nodes 201 and202 is the following. The case of a positive overvoltage is consideredas an example. As in normal operation, the circuit 300-1 associated withtransistor 209 is equivalent to an open circuit between its terminals301 and 302, and transistor 209 is on. Further, as soon as the voltagebetween node 202 and node 201 becomes greater than the threshold of thecircuit 300-1 associated with transistor 208, a current flows throughdipoles D1 and D2 and through the resistors R3 and R4 of the circuit. Assoon as the voltage drop in resistor R4 is greater than the thresholdvoltage of transistor T, the latter turns on and a current flows betweennodes 403 and 401, not only via resistor R4 and R3 and dipole D1, butalso via transistor T. Thus, as soon as the voltage between node 202 andnode 201 becomes greater than the threshold of circuit 300-1 associatedwith transistor 208, the gate potential of transistor 208 increases withthe potential of node 202. In particular, once the transistor T ofcircuit 300-1 is conductive, the potential on the gate of transistor 208is equal to the potential of node 202 minus the threshold voltage oftransistor T, the voltage drop in resistor R3, and the voltage drop inthe dipoles D1 and D2 of circuit 300-1.

In the example of FIG. 4-1, the threshold of each circuit 300-1 is equalto the sum of the reverse turn-on threshold of dipole D1 and of theforward turn-on threshold of dipole D2. Further, in each circuit 300-1,transistor T switches to the on state when the voltage between terminals301 and 302 of the circuit exceeds the sum of the reverse turn-onthreshold of dipole D1, of the forward turn-on threshold of dipole D2,and of the threshold voltage of transistor T.

The operation of bridge 4-1 in case of a negative overvoltage betweennodes 201 and 202 can be deduced, by symmetry, from the operationdescribed hereinabove in case of a positive overvoltage.

An advantage of a circuit 300-1 over a circuit 300 is that it enables toconduct, once its transistor T is on, a greater current between itsterminals 301 and 302, whereby the potential on the gate of transistor208 or 209 associated therewith is higher.

Another advantage of circuit 300-1 over a circuit 300 is that, once thetransistor T of the circuit is on, the current in dipole D1 is smaller.This is particularly advantageous when dipole D1 is not configured toconduct a significant current and/or when the internal resistor ofdipole D1 is high.

Although this is not shown in FIG. 4, in each circuit 300-1, a frequencycompensation capacitor may be provided between nodes 401 and 403 and/ora frequency compensation capacitor may be provided between nodes 401 and402. Such capacitors allow a faster response of circuit 300-1 in case ofan overvoltage. However, the value of each of these capacitors ispreferably selected to be relatively low, for example, lower than 1 pF,to avoid disturbing the operation of bridge 4-1 in the absence of anovervoltage between pads 101 and 102.

FIG. 5 illustrates, in the form of a circuit, a portion of a device 3-2comprising a rectifying bridge 4-2 according to still anotherembodiment.

Device 3-2 is similar to the device 3-1 of FIG. 4, only the differencesbetween devices 3-2 and 3-1 being here detailed. More particularly,device 3-2 differs from device 3-1 by its voltage rectifying bridge 4-2,rectifying bridge 4-2 comprising a turn-on circuit 300-2 instead of eachcircuit 300-1 of rectifying bridge 4-1. Each circuit 300-2 comprises afirst terminal 301, a second terminal 302 and, in this embodiment, athird terminal 303. The circuit 300-2 associated with transistor 208,respectively 209, has its terminal 301 connected to the drain oftransistor 208, respectively 209, its terminal 302 connected to the gateof transistor 208, respectively 209, and its terminal 303 connected tonode 201, respectively 202.

Each circuit 300-2 comprises a branch comprising a first dipole with adiode function D1 and a second dipole with a diode function D2 coupledtogether in anti-series.

In this embodiment, in each circuit 300-2, the branch comprising dipolesD1 and D2 in anti-series is connected between terminals 301 and 303 ofthe circuit. In each circuit 300-2, the branch comprising dipoles D1 andD2 in anti-series further comprises a resistor R4 series-connected todipoles D1 and D2. Each circuit 300-2 further comprises a transistor Thaving a control terminal connected to a terminal 502 of resistor R4,having a conduction terminal 503 coupled to terminal 301 of circuit300-2, and having another conduction terminal 504 coupled to terminal302 of circuit 300-2. Each circuit 300-2 is configured so that a voltagedrop in its resistor R4 conditions a turning-on of its transistor T.

According to an embodiment, as illustrated in FIG. 5, in each circuit300-2, transistor T is a P-channel MOS transistor having its source 503coupled to the terminal 301 of circuit 300-2, and its drain 504 coupledto the terminal 302 of the circuit. The terminal of resistor R4 oppositeto terminal 502 is then connected to the terminal 503 of transistor T.Preferably, the body region of transistor T is coupled to the source oftransistor T, so that the body and source regions of transistor T are atthe same potential. According to an alternative embodiment, notillustrated, in each circuit 300-2, transistor T is replaced with a PNPbipolar transistor having its base forming a control terminal of thetransistor and connected to terminal 502 of resistor R4, having itsemitter 503 coupled to the terminal 301 of circuit 300-2, and having itscollector 505 coupled to the terminal 302 of circuit 300-2. In thisvariation, the terminal of resistor R4 opposite to terminal 502 is thenconnected to the emitter 503 of the transistor.

According to an embodiment, as illustrated in FIG. 5, in each circuit300-2, the terminal 503 of transistor T is connected to the terminal 301of circuit 300-2, and dipole D2 is connected between the terminal 503 oftransistor T and the terminal 303 of circuit 300-2, for example, withits cathode on the side of terminal 303 of the circuit, for example,connected to terminal 303. Circuit 300-2 then further comprises a dipolewith a diode function D3 series-connected to transistor T, betweenterminal 503 of transistor T and terminal 302, preferably between theterminal 504 of transistor T and the terminal 302 of circuit 300-2, thecathode of dipole D3 for example being connected to terminal 302 ofcircuit 300-2. Dipole D3 is configured to block a current betweenterminals 301 and 302 of circuit 300-2 when the voltage between theterminal 301 of circuit 300-2 and the terminal 301 of the other circuit300-2 is smaller than the threshold of this circuit. In other words,dipole D3 is configured to block the current between the terminals 301and 302 of circuit 300-2 when the bridge is in normal operation, thatis, particularly, when the potential on terminal 302 is greater than thepotential on the terminal 301 of this circuit.

The normal operation of bridge 4-2 is similar to that of thepreviously-described bridge 4 (FIG. 3). In particular, in each circuit300-2, no current flows through the dipoles D1, D2, and D3 of circuit300-2, whereby no current flows between the terminal 301 of circuit300-2 and each of the terminals 302 and 303 of the circuit.

The operation of bridge 4-2 during an overvoltage between nodes 201 and202 is the following. The case of a positive overvoltage is consideredas an example. As in normal operation, the circuit 300-2 associated withtransistor 209 is equivalent to an open circuit between its terminals301 and 302, and transistor 209 is on. Further, as soon as the voltagebetween node 202 and node 201 becomes greater than the threshold of thecircuit 300-2 associated with transistor 208, a current flows throughthe circuit dipoles D1 and D2, and thus through resistor R4. As soon asthe voltage drop in resistor R4 is greater than the threshold voltage oftransistor T, the latter switches to the on state and a current flowsbetween the terminals 301 and 302 of the circuit, and thus throughresistor R4. As a result, the gate potential of transistor 208 increaseswith the potential of node 202. In other words, the potential on thegate of transistor 208 is then equal to the potential of node 202 minusthe voltage drop between the terminals 503 and 504 of transistor T andthe voltage drop in dipole D3. In the example of FIG. 5, the thresholdof each circuit 300 is equal to the sum of the reverse turn-on thresholdof dipole D1, of the forward turn-on threshold of dipole D2, and of thethreshold voltage of transistor T.

As an example, the case where dipoles D2 and D3 have a forward turn-onthreshold equal to 0.6 V and dipole D1 has a reverse turn-on thresholdequal to 5 V is considered. In this case, when a current flows fromterminal 301 to terminal 302 due to the fact that the voltage betweenterminals 301 and 303 (referenced to terminal 303) is greater than thethreshold of circuit 300-2, the voltage on the gate of transistor T mayat most be equal to 5.6 V, that is, the sum of the forward turn-onthreshold of dipole D2 and of the reverse turn-on threshold of dipoleD1. Resistor R4 then withstands the difference between the voltage onthe gate of transistor T and the voltage on terminal 301. Oncetransistor T is on, the voltage drop between terminals 301 and 302 isequal to the forward turn-on threshold of dipole D3, neglecting thevoltage drop between the conduction terminals of transistor T. Thus, thevoltage on terminal 302 is then equal to the voltage on node 202 minusthe 0.6 V in D3, and may be equal to 6.4 V when the voltage on node 202is 7 V. By using such examples of numerical values in the case of FIG.4, the voltage on terminal 302 of the circuit is at most equal to thevoltage on node 202 minus the sum of the forward turn-on threshold ofD2, of the reverse turn-on threshold of D1, and of the turn-on thresholdof transistor T, for example, equal to 0.7 V, which results in a voltageon terminal 302 equal to 0.7 V and much smaller than that of the case ofFIG. 5.

The operation of bridge 4-2 in case of a negative overvoltage betweennodes 201 and 202 can be deduced, by symmetry, from the operationdescribed hereinabove in case of a positive overvoltage.

In an alternative embodiment, not illustrated, in each circuit 300-2,dipole D2 is connected between the terminal 301 of circuit 300-2 and theterminal 503 of transistor T, for example, with the anode of dipole D2connected to terminal 301. In this variant, the terminal 504 oftransistor T is connected to the terminal 302 of circuit 300-2. Further,in this variation, dipole D3 may be omitted, its current blockingfunction being ensured by dipole D2. However, in the present variant, itmay be useful to modify the connection of the body region of transistorT to avoid, in normal operation, when the potential of terminal 302 isgreater than the potential of terminal 301, for the drain-body diode oftransistor T to be forward conductive and to possibly turn on the NPNbipolar transistor of transistor T having its emitter corresponding tothe drain of transistor T, its base corresponding to an N-type wellhaving transistor T formed therein and its collector corresponding tothe P-type substrate having the N-type well formed therein. For example,it may then be provided for transistor T to be associated with two MOStransistors cross-connected between the source and the drain oftransistor T, to ensure that the N well of transistor T is at the lowerof the two source and drain potentials of transistor T.

It will be within the abilities of those skilled in the art to describethe operation of bridge 4-2 according to this variation, based on theabove-described operation.

An advantage of the above-described embodiments and variants of circuit300-2 over a circuit 300-1 is that it enables, once its transistor T ison, to decrease the voltage drop between its terminals 301 and 302. As aresult, the potential on the gate of the transistor 208 or 209associated therewith it higher.

Although this is not shown in FIG. 5, a frequency compensation capacitormay be provided in parallel with dipole D1 and/or a frequencycompensation capacitor may be provided in parallel with transistor T.Such capacitors allow a faster response of circuit 300-2 in case of anovervoltage. However, the value of each of these capacitors ispreferably selected to be relatively low, for example, lower than 1 pF,to avoid disturbing the operation of bridge 4-2 in the absence of anovervoltage between pads 101 and 102.

FIG. 6 illustrates, in the form of a circuit, a portion of a device 3-3comprising a rectifying bridge 4-3 according to still anotherembodiment.

Device 3-3 is similar to the device 3-1 of FIG. 4, only the differencesbetween devices 3-3 and 3-1 being here detailed. More particularly,device 3-3 differs from device 3-1 by its voltage rectifying bridge 4-3,rectifying bridge 4-3 comprising a turn-on circuit 300-3 instead of eachcircuit 300-1 of rectifying bridge 4-1. Each circuit 300-3 comprises afirst terminal 301 and a second terminal 302. The circuit 300-3associated with transistor 208, respectively 209, has its terminal 301connected to the drain of transistor 208, respectively 209, and itterminal 302 connected to the gate of transistor 208, respectively 209.

Each circuit 300-3 comprises a branch comprising a first dipole with adiode function D1 and a second dipole with a diode function D2 coupledtogether in anti-series.

In this embodiment, in each circuit 300-3, the branch comprising dipolesD1 and D2 in anti-series is connected between the terminals 301 and 302of the circuit. In each circuit 300-3, the branch comprising dipoles D1and D2 in anti-series further comprises a resistor R3 series-connectedto the first dipole D1 between a node 601 and a node 602 and a resistorR4 connected between node 602 and a node 603. Each circuit 300-3 furthercomprises a transistor Tb having a control terminal connected to node602 and having conduction terminals respectively connected to nodes 601and 603. Each circuit is configured so that a voltage drop in itsresistor R4 conditions a turning-on of its transistor Tb.

According to an embodiment, as illustrated in FIG. 6, in each circuit300-3, transistor Tb is an NPN bipolar transistor, the emitter and thecollector of transistor Tb then being coupled, preferably connected,respectively to nodes 603 and 601. In an alternative embodiment, notillustrated, in each circuit 300-3, bipolar transistor Tb is replacedwith an N-channel MOS transistor having its gate forming a controlterminal of the transistor connected to node 602, having its sourceconnected to node 603, and having its drain connected to node 601.Preferably, the body region of the MOS transistor is then coupled to thesource of the transistor, so that the body and source regions of thetransistor are at the same potential.

According to an embodiment, as illustrated in FIG. 6, in each circuit300-3, dipole D2 is connected between node 603 and the terminal 302 ofcircuit 300-2, the cathode of dipole D2 being for example connected tothe terminal 302 of circuit 300-1. In an alternative embodiment, notillustrated, in each circuit 300-2, dipole D2 is connected betweenterminal 301 and the node 601 of circuit 300-3, the anode of dipole D2being for example connected to the terminal 301 of circuit 300-3.

The normal operation of bridge 4-3 is similar to that of thepreviously-described bridge 4 (FIG. 3). In particular, in each circuit300-3, when no current flows through dipoles D1 and D2 of circuit 300-3,the voltage across resistor R4 is zero, and transistor Tb is off. Thus,no current flows between the terminals 301 and 302 of circuits 300-3,nor in resistors R1 and R2.

The operation of bridge 4-3 during an overvoltage between nodes 201 and202 is the following. The case of a positive overvoltage is consideredas an example. As in normal operation, the circuit 300-3 associated withtransistor 209 is equivalent to an open circuit between its terminals301 and 302, and transistor 209 is on. Further, as soon as the voltagebetween node 202 and node 201 becomes greater than the threshold of thecircuit 300-3 associated with transistor 208, a current flows throughdipoles D1 and D2 of the circuit and through resistor R4. As soon as thevoltage drop in resistor R4 is greater than the threshold voltage oftransistor Tb, a current flows between nodes 601 and 603, not only viaresistors R3 and R4 and dipole D1, but also via transistor Tb. As aresult, as soon as the voltage between node 202 and node 201 becomesgreater than the threshold of circuit 300-3, the gate potential oftransistor 208 increases with the potential of node 202. In particular,as soon as the transistor Tb of circuit 300-3 is on, the potential onthe gate of transistor 208 is then equal to the potential of node 202minus the threshold voltage of transistor Tb, the voltage drop inresistor R3, and the voltage drop in dipoles D1 and D2 of circuit 300-3.

In the example of FIG. 6-3, the threshold of each circuit 300-3 is equalto the sum of the reverse turn-on threshold of dipole D1 and of theforward turn-on threshold of dipole D2. Further, transistor Tb switchesto the on state as soon as the voltage between terminals 301 and 302 ofthe circuit exceeds the sum of the reverse turn-on threshold of dipoleD1, of the forward turn-on threshold of dipole D2, and of the thresholdof transistor Tb.

The operation of bridge 4-3 in case of a negative overvoltage betweennodes 201 and 202 can be deduced, by symmetry, from the operationdescribed hereinabove in case of a positive overvoltage.

An advantage of a circuit 300-3 over a circuit 300 is that it enables toconduct, once its transistor Tb is on, a more significant currentbetween its terminals 301 and 302, whereby the potential on the gate ofthe transistor 208 or 209 associated therewith is higher.

Although this is not shown in FIG. 6, in each circuit 300-3, a frequencycompensation capacitor may be provided between nodes 601 and 603 and/ora frequency compensation capacitor may be provided between nodes 601 and602. Such capacitors allow a faster response of circuit 300-3 in case ofan overvoltage. However, the value of each of these capacitors ispreferably selected to be relatively low, for example, lower than 1 pF,to avoid disturbing the operation of bridge 4-3 in the absence of anovervoltage between pads 101 and 102.

According to an embodiment, the dipoles D1 of the previously-describedcircuits 300-1, 300-2, and 300-3 are implemented by a single Zenerdiode.

According to another embodiment, the dipoles D1 of thepreviously-described circuits 300, 300-1, 300-2, and 300-3 areimplemented by means of a plurality of Zener diodes in parallel, whichenables to decrease the inner resistance of dipole D1 and thus thevoltage drop between its terminals when a current flows therethrough.

According to still another embodiment, the dipoles D1 of thepreviously-described circuits 300, 300-1, 300-2, and 300-3 areimplemented by means of a plurality of MOS transistors in series, eachdiode-assembled, that is, with its drain and its gate connectedtogether, the transistor drains being on the side of the dipole cathode.This enables to decrease or to more finely adjust the reverse turn-onthreshold of dipoles D1, and thus of circuits 300, 300-1, 300-2, and300-3, at the cost of an increase in the internal resistance of dipolesD1. The dipoles D1 of circuits 300, 300-1, 300-2, and 300-3, and thepossible dipole D3 of circuit 300-2 are each implemented by means of adiode or of a diode-assembled MOS transistor.

To protect device 1 against overvoltages, rather than providing circuits300, 300-1, 300-2, and 300-3, it could have been devised to place anovervoltage protection between each of pads 101 and 102 and node 210 atthe ground potential. However, the provision of such protections wouldhave led to a device having a larger surface area than that of devices3, 3-1, 3-2, and 3-3. Further, such protections would have introducedstray capacitances and resistances on each of pads 101 and 102, whichwould have disturbed the operation of the rectifying bridge in theabsence of an overvoltage.

According to an embodiment where device 3, 3-1, 3-2, or 3-3 comprises aretromodulation MOS transistor connected between its pads 101 and 102,it may be provided for two circuits 300, 300-1, 300-2, or 300-3,respectively, to be associated with the retromodulation transistor, toturn it on when an overvoltage occurs on one or the other of pads 101and 102. A first one of the two circuits 300, 300-1, 300-2, or 300-3then has its terminal 301 connected to pad 102, its possible terminal303 connected to pad 101, and its terminal 302 connected to the gate ofthe retromodulation transistor and coupled to pad 101 by a resistor. Thesecond one of the two circuits then has its terminal 301 connected topad 101, its possible terminal 303 connected to pad 102, and itsterminal 302 connected to the gate of the retromodulation transistor andcoupled to pad 102 by another resistor.

Although this is not claimed herein, two turn-on circuits may beassociated with the retromodulation transistor, as describedhereinabove, without for transistors 208 and 209 to be each associatedwith a turn-on circuit.

According to embodiments, not illustrated, the turn-on circuits of asame device 3, 3-1, 3-2, or 3-3 may be different from one another,including when such circuits are associated with the retromodulationtransistor. For example, the circuit 300 of the bridge 3 associated withtransistor 208 may be replaced with a circuit 300-1, 300-2, or 300-3.

According to an embodiment, rectifying bridge 4, 4-1, 4-2, or 4-3 andpads 101 and 102 of device 3, 3-1, 3-2, or 3-3 respectively belong to asame integrated circuit, the conductive antenna winding being preferablyexternal to the integrated circuit.

Although wireless communication devices 3, 3-1, 3-2, and 3-3, forexample, NFC-type (near field communication) devices or devices inaccordance with ISO standard 14443 or 15693, have been described herein,rectifying bridges 4, 4-1, 4-2, and 4-3 may be implemented in otherdevices, to protect circuits of these other devices from possibleovervoltages, for example caused by electrostatic discharges, on one orthe other of two pads having the respective nodes 201 and 202 of therectifying bridges coupled thereto.

Further, it will be within the abilities of those skilled in the art toadapt the above disclosure to the case where transistors 208 and 209have a P channel, for example, by inverting all the N and P types andthe values of the previously-described voltages, for example, byreplacing each N-channel MOS transistor, respectively, with a P-,respectively N-channel MOS transistor, by replacing each NPN,respectively PNP transistor, with a PNP, respectively NPN, transistor,by replacing a P substrate of the circuit coupled to the lowestpotential with an N substrate coupled to the highest potential, etc. Inthis case, the threshold of a turn-on circuit is negative and is, inabsolute value, equal to the threshold of the turn-on circuits describedin relation with FIGS. 2 to 6. The voltage between the terminal 301 ofthis circuit and the terminal 301 of the other turn-on circuit is thencalled greater than the threshold of the circuit if it has the same signas the threshold and an absolute value greater than the absolute valueof the threshold. In other words, whether transistors 208 and 209 havean N channel or a P channel, a turn-on circuit is configured toelectrically couple its terminals 301 and 302 when the voltage betweenthe terminal 301 of this circuit and the terminal 301 of the othercircuit has the same sign as the circuit threshold and has an absolutevalue greater than that of the threshold, and to isolate its terminals301 and 302 when the voltage between the terminal 301 of the circuit andthe terminal 301 of the other turn-on circuit has an absolute valuesmaller than that of the threshold and, also, when this voltage is hassign opposite to that of the circuit threshold.

Various embodiments and variants have been described. Those skilled inthe art will understand that certain features of these embodiments canbe combined and other variants will readily occur to those skilled inthe art.

Finally, the practical implementation of the described embodiments andvariations is within the abilities of those skilled in the art based onthe functional indications given hereinabove. In particular, it will bewithin the abilities of those skilled in the art to select theresistance values, the values of the possible frequency compensationcapacitances, the forward turn-on threshold of dipole D2, the forwardturn-on threshold of the possible dipole D3, and/or the reverse turn-onthreshold of dipole D1 according to the targeted application, that is,according to the maximum voltage capable of being present between nodes201 and 202 in normal operation (with no overvoltage) and/or to themaximum amplitude of the overvoltages capable of occurring between nodes201 and 202. As an example, the values of resistances R1 and R2 shouldbe sufficiently low to avoid disturbing the bridge in normal operationby introducing R*C-type propagation delays (C being the capacitance ofthe gates of transistors 208 and 209), for example, smaller than 10 kΩ,and should be sufficiently high to enable the turn-on circuits toincrease the voltage on the gate of transistors 208 and 209, forexample, greater than 100Ω, resistances R1 and R2 for example eachhaving a value in the order of 1 kΩ, for example, equal to 1 k.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andthe scope of the present invention. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting. The present invention is limited only as defined in thefollowing claims and the equivalents thereto.

What is claimed is:
 1. A device comprising a rectifying bridgecomprising: a first branch connected between first and second inputnodes of the bridge and comprising a third output node of the bridge; asecond branch comprising first and second metal oxide semiconductor(MOS) transistors series-connected between the first and second inputnodes, wherein sources of the first and second transistors are coupledto a fourth output node of the bridge; a first resistor connectedbetween a gate of the first transistor and the second input node; asecond resistor connected between a gate of the second transistor andthe first input node; and for each of the first and second transistors,a circuit associated with the respective transistor comprises a firstterminal connected to a drain of the respective transistor and a secondterminal connected to the gate of the respective transistor, wherein thecircuit is configured to electrically couple its first and secondterminals when an absolute value of a voltage between the first terminalof the circuit and the first terminal of the other circuit is greaterthan or equal to an absolute value of a threshold of the circuit and thevoltage has a same sign as the threshold.
 2. The device according toclaim 1, wherein each circuit is further configured to electricallyisolate its first and second terminals when the absolute value of thevoltage between the first terminal of the circuit and the first terminalof the other circuit is smaller than the absolute value of the thresholdof the circuit and also when the voltage has a sign opposite to the signof the threshold of the circuit.
 3. The device according to claim 1,wherein the first branch of the bridge comprises third and fourth MOStransistors series-connected between the first and second input nodesand each diode-assembled, and sources of the third and fourthtransistors are connected to the third output node.
 4. The deviceaccording to claim 3, wherein the first, second, third, and fourthtransistors have a same N- or P-type channel.
 5. The device according toclaim 1, wherein each circuit comprises a branch comprising a firstdipole with a first diode function and a second dipole with a seconddiode function coupled in anti-series, one end of the branch beingconnected to the first terminal of the circuit and another end of thebranch being coupled to the first terminal of the other circuit.
 6. Thedevice according to claim 5, wherein, in each circuit, the first andsecond dipoles are configured to block a current when the absolute valueof the voltage between the first terminal of the circuit and the firstterminal of the other circuit is smaller than the absolute value of thethreshold of the circuit and when the voltage has a sign opposite to thesign of the threshold of the circuit, and to conduct the current whenthe absolute value of the voltage between the first terminal of thecircuit and the first terminal of the other circuit is greater than orequal to the absolute value of the threshold of the circuit and thevoltage has the same sign as the threshold.
 7. The device according toclaim 6, wherein each circuit is configured so that the conduction ofthe current in the first dipole of the circuit causes an electriccoupling of the first and second terminals of the circuit.
 8. The deviceaccording to claim 5, wherein, in at least one of the circuits, theanother end of the branch of the circuit is connected to the secondterminal of the circuit.
 9. The device according to claim 8, wherein, inthe at least one of the circuits, the branch of the circuit comprises:fifth, sixth, and seventh nodes; a third resistor series-connected tothe first dipole between the fifth node and the sixth node; and a fourthresistor connected between the sixth node and the seventh node, eachcircuit further comprising a fifth transistor having a control terminalconnected to the sixth node and having conduction terminals respectivelyconnected to the fifth node and to the seventh node, a voltage drop inthe fourth resistor conditioning a turning-on of the fifth transistor.10. The device according to claim 9, wherein, in the at least one of thecircuits: the second dipole is connected between the first terminal ofthe circuit and the fifth node, the seventh node being connected to thesecond terminal of the circuit; or the second dipole is connectedbetween the seventh node and the second terminal of the circuit, thefifth node being connected to the first terminal of the circuit; or thesecond dipole is connected between the first terminal of the circuit andthe seventh node, the fifth node being connected to the second terminalof the circuit; or the second dipole is connected between the fifth nodeand the second terminal of the circuit, the seventh node being connectedto the first terminal of the circuit.
 11. The device according to claim5, wherein, in at least one of the circuits, the another end of thebranch of the circuit is connected to a third terminal of the circuit,the third terminal of the circuit being connected to the first terminalof the other circuit.
 12. The device according to claim 11, wherein, inthe at least one of the circuits, the branch comprises a third resistorin series with the first and second dipoles, each circuit furthercomprising a fifth transistor having a control terminal connected to aterminal of the third resistor, having a first conduction terminalcoupled to the first terminal of the circuit, and having a secondconduction terminal coupled to the second terminal of the circuit, avoltage drop in the third resistor conditioning a turning-on of thefifth transistor.
 13. The device according to claim 12, wherein, in theat least one of the circuits, the second dipole is connected between thefirst terminal of the circuit and the first conduction terminal of thefifth transistor, the second conduction terminal of the fifth transistorbeing connected to the second terminal of the circuit.
 14. The deviceaccording to claim 12, wherein at least one of the circuits, furthercomprises a third dipole with a diode function series-connected to thefifth transistor of the circuit between the first and second terminalsof the circuit, the third dipole being connected to the second terminalof the circuit and the branch of the circuit being connected between thefirst and third terminals of the circuit.
 15. The device according toclaim 5, wherein the first dipole is a Zener diode, a plurality of Zenerdiodes connected in parallel, or a plurality of series-connected MOStransistors configured as diodes.
 16. An integrated circuit (IC)comprising: first and second input pads; and a rectifying bridgecomprising: a first branch connected between first and second input padsof the bridge and comprising a third output node of the bridge; a secondbranch comprising first and second metal oxide semiconductor (MOS)transistors series-connected between the first and second input pads,wherein sources of the first and second transistors are coupled to afourth output node of the bridge; a first resistor connected between agate of the first transistor and the second input pad; a second resistorconnected between a gate of the second transistor and the first inputpad; and for each of the first and second transistors, a circuitassociated with the respective transistor comprises a first terminalconnected to a drain of the respective transistor and a second terminalconnected to the gate of the respective transistor, wherein the circuitis configured to electrically couple its first and second terminals whenan absolute value of a voltage between the first terminal of the circuitand the first terminal of the other circuit is greater than or equal toan absolute value of a threshold of the circuit and the voltage has asame sign as the threshold.
 17. The IC of claim 16, wherein each circuitis further configured to electrically isolate its first and secondterminals when the absolute value of the voltage between the firstterminal of the circuit and the first terminal of the other circuit issmaller than the absolute value of the threshold of the circuit and alsowhen the voltage has a sign opposite to the sign of the threshold of thecircuit.
 18. The IC of claim 16, wherein the first branch of the bridgecomprises third and fourth MOS transistors series-connected between thefirst and second input nodes and each diode-assembled, and sources ofthe third and fourth transistors are connected to the third output node.19. The IC of claim 16, wherein each circuit comprises a branchcomprising a first dipole with a first diode function and a seconddipole with a second diode function coupled in anti-series, one end ofthe branch being connected to the first terminal of the circuit andanother end of the branch being coupled to the first terminal of theother circuit.
 20. The IC of claim 16, wherein the first and second padsare configured to be coupled to respective ends of a conductive windingof an antenna.